1. Field
Exemplary embodiments relate to an annealing apparatus and method for a float glass, and more particularly, to an annealing apparatus and method for a float glass in which a sealing structure of lehr rolls of an annealing lehr which anneals a glass ribbon continuously produced by a floating process.
2. Description of the Related Art
Generally, a float glass manufacturing system continuously supplies molten glass onto a molten metal (e.g., a molten tin) stored in a float bath, molds a strip-shaped (or, ribbon-shaped) glass ribbon with consistent width and thickness while carrying the molten glass to float on the molten metal, and pulls the glass ribbon toward an annealing lehr adjacent to the outlet of the float bath to produce a glass plate.
Here, the molten metal may be for example a molten tin or a molten tin alloy and has a greater specific weight than the molten glass. The molten metal is received in a float chamber filled with reducing hydrogen (H2) and/or nitrogen (N2) In addition, the float bath receiving the molten metal is elongated in a length direction and includes special fireproof material. The molten glass moves from an upstream side of the float bath to a downstream side and is molded into a glass ribbon on the surface of the molten metal. Then, at a separating location (hereinafter, referred to as a “take-off point”) set at the downstream side of the float bath, the glass ribbon is lifted up away from the molten metal by lift-out rollers installed to a dross box, and the lifted glass ribbon is delivered through the dross box toward an annealing lehr for the next process. Meanwhile, a successive glass ribbon with a predetermined width is cut into several sheets with a predetermined size, which are called “glass sheets”.
The gas containing volatile tin and contained in the float bath flows toward the downstream side of the float bath, namely toward the dross box, due to a positive pressure in the float bath. The gas flowing toward the dross box as mentioned above creates inferiorities at the surface of the molten tin or the surface of the glass which is carried after being condensed near the dross box and at a low-temperature region in the float bath at the downstream side (generally, dross is generated at 780° C. or below). In addition, even though the inside of the float bath is kept with a positive pressure, the tin-containing gas mentioned above may flow toward the downstream side of the float bath through the dross box. In this process, oxygen contained in an external air may react with the volatile tin in the float bath at the relatively low-temperature region, and if the gas is condensed in this state, a tin-based floating impurity may be generated at the surface of the tin. In this case, while the ribbon-shaped glass is lifted up by the lift-out rollers and drawn out of the float bath, the tin-based floating impurity adhered to the surface of the molten tin is moved and drawn together with the bottom surface of the glass ribbon. This tin-based floating impurity may contaminate the dross box and the surface of rollers used in the annealing process. In addition, in a case where the glass moves by the float bath or is annealed, the tin-based floating impurity may be a potential factor of an impurity forming at the bottom surface. Therefore, the tin-based floating impurity may deteriorate the safety of the annealing work and deteriorate the process stability and the quality of the glass products.
In addition, in the conventional float glass manufacturing apparatus, sulfurous acid gas is supplied into the annealing lehr. The sulfurous acid gas reduces the friction between the bottom of the glass ribbon and the lehr rolls to prevent any defect of a glass product. However, since the space between the lehr rolls and a casing of the annealing lehr to which the lehr rolls are installed is very wide, the sulfurous acid gas may leak to the space and give harm to the human body.